The invention relates to the field of arrayed waveguide grating (AWG), and in particular to an AWG device using an input structure comprising of an array of coupled waveguides.
AWGs can be useful in many optical communication applications where wavelength-specific filtering and processing are required. Unlike the legacy TDM systems, AWGs function purely in the optical domain when filtering the independent wavelength bands and thus do not require expensive, electrical up/down conversion. As all-optical wavelength filtering components, AWGs have become attractive for optical communication systems. However, as with any component, many technical and economic factors impact the viability of AWGs in the market.
AWGs are thin, fragile chips with narrow waveguides produced using planar lightwave circuit (PLC) processing techniques. The waveguides can be fabricated by forming (e.g., etching) waveguide core patterns over a substrate and undercladding. A doped glass overcladding (e.g., boro-phosphate silicate glass or BPSG) is then formed over the cores, to complete the waveguide formation. As an “integrated” PLC component in a fiber optic system, the optical signals are usually coupled (e.g., at the chip edge) between input and output fiber optics and the on-chip waveguides, leading to concerns about the device's end-to-end insertion loss.
Since the mode of a waveguide can extend past the core as an evanescent tail, the mode in one waveguide may actually excite a field in a neighboring waveguide. The mathematics that describes this coupling is known as coupled mode theory. The effects can be harmful, causing closely spaced waveguides to couple into one another and destroying the original intention of a device. However, the effects can also be useful. In particular, coupled mode theory can be used to spread light from the input waveguide to the entire array in a uniform or Gaussian distribution.